Experimental observations ofs−pcoupling in copper dimer anions

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The photoelectron velocity-map image technique was employed to examine the one-photon detachment of Cu monomer and dimer anions using a linearly polarized infrared femtosecond laser. While the photoelectron angular distribution (PAD) in a single-photon detachment experiment of Cu${}^{\ensuremath{-}}$ shows no dependence on photon energy, the dimer anion PAD does show a strong dependence on photon energy. As the laser wavelength increases from 532 to 817 nm, the photoelectron angular distributions of the main one-photon detachment channel of the prominent detachment channel of Cu${}_{2}$${}^{\ensuremath{-}}$ changes its direction from parallel to the direction of polarization for the 532-nm laser to perpendicular to the direction of polarization for the 817-nm laser. Based upon a numerical analysis of the anisotropy parameters, the relative contributions of the $s$, $p$, and $d$ orbitals are obtained. The fully occupied $d$ orbitals contribute less to the detachment amplitude. The contribution of the $p$ waves to the detachment amplitude increases with the photon energy, while that of $s$ waves decreases, which is in agreement with the prediction of the Wigner threshold law. The relative contributions of the different partial waves, $s$ and $p$, to the detachment amplitude are altered by the excess energy of the detached electron, resulting in the determined shape of the photoelectron angular distributions. Our one-photon photodetachment experiments on the energy-dependent angular distributions of the copper anionic dimers indicate that $s$-$p$ coupling is important to the photodetachment of copper dimer anions, especially at increased photon energies.